The present invention belongs to a pretensioner which is used, for example, in a seat belt device attached to the seat of a vehicle, such as a car. The pretensioner typically applies a tension on a seat belt and increases the restraint force on the occupant in the case of an emergency such as, for example, a vehicle collision. More particularly, the present invention relates to a pretensioner in which a piston is operated by the pressure of gas generated by a gas generator so as to apply a tension to a seat belt.
Conventionally, the seats of vehicles, such as cars, are provided with seat belt devices, and the seat belt devices serve to protect the occupant by restraining the occupant with the seat belt and reducing the inertial movement of the occupant when an extremely high vehicle deceleration is caused in the case of an emergency such as a vehicle collision. Some of such conventional seat belt devices have a pretensioner that quickly restrains the occupant with a great restraint force by tensioning the seat belt to increase the restraint force in the above emergency. While the pretensioner is generally disposed in a seat-belt retractor of the seat belt device, it is sometimes disposed in a buckle or a lap anchor.
For example, a seat belt device having a buckle pretensioner is disclosed in Japanese Unexamined Patent Application Publication No. 2000-326823 (incorporated by reference herein). This publication discloses two types of buckle pretensioners. In the first type, a buckle is pulled by the pulling of a connecting member for connecting the buckle and a piston into a cylinder, in which the piston slides, when actuated. In the buckle pretensioner, a gas generator is mounted on a base and a piston and a cylinder are attached to the gas generator. A middle portion of the connecting member is curved by a pulley mounted in the base so as to change the direction thereof. The buckle-pulling direction and the piston-sliding direction are set to form a predetermined angle therebetween. When the buckle pretensioner is actuated, the piston is operated by the pressure of gas generated by the gas generator to draw the connecting member, so that the buckle is pulled.
In the second type of buckle pretensioner, when actuated, a connecting member for connecting a buckle and a base is pressed by a piston, and the buckle is thereby pulled. A piston and a cylinder are mounted on a base and a gas generator is disposed in the cylinder. A middle portion of the connecting member is curved by a pulley disposed in a piston rod so as to change the direction thereof, and the buckle-pulling direction and the piston-sliding direction are set to form a predetermined angle therebetween. When the buckle pretensioner is actuated, the piston is operated by the pressure of gas generated by the gas generator, and the pulley presses the connecting member, so that the buckle is pulled.
In both the first and second types of buckle pretensioners disclosed in the aforementioned publication, a pressure vessel for accommodating the gas generator, and the cylinder in which the piston slides are made of separate components. As a result, the number of components and the number of assembly processes increase, and the cost is increased. In particular, the pressure vessel of the first type is generally made by die-casting in zinc in order to ensure pressure strength, and for this reason, both the weight and thickness thereof are increased.
A seat belt device having a buckle pretensioner in which a pressure vessel and a cylinder are formed of a single component is disclosed in Japanese Unexamined Patent Application Publication No. 2001-39268 (incorporated by reference herein). In the buckle pretensioner disclosed in this publication, a buckle and a piston are connected by a connecting member, and the piston is slidably fitted in one case. Further, a gas generator is fixed by a fixing member inside the case so that it is coaxial with the sliding axis of the piston. A middle portion of the connecting member is bent by a lock member rotatably disposed so as to change the direction thereof, and the buckle-pulling direction and the piston-sliding direction are set to form a predetermined angle therebetween. When the buckle pretensioner is actuated, the piston is operated by the pressure of gas generated by the gas generator so as to draw the connecting member, so that the buckle is pulled.
Since the pressure vessel for the gas generator and the cylinder are thus formed of a single component, the number of components and the number of assembly processes are reduced, and the cost is thereby reduced.
However, in the buckle pretensioner disclosed in Japanese Unexamined Patent Application Publication No. 2001-39268, the gas generator is fixed by the fixing member inside the case so that it is offset from the piston toward the buckle and is coaxial with the sliding axis of the piston, as a result the connecting member for connecting the buckle and the piston needs to be positioned to avoid interference with the gas generator and, therefore, the connecting member and the gas generator are placed in parallel. However, when the connecting member and the gas generator are placed in parallel, the cross-sectional area of the case is large. Accordingly, in order to prevent the cross-sectional area of the case from becoming large, it is essential to use a gas generator having a special shape that is different from the shape of the conventional gas generator, for example, the shape of an elongated straw. For this reason, it is not preferred to use standard-shape gas generators that have been used heretofore.